GB919023A - Improvements in or relating to data stores - Google Patents

Abstract

919,023. Magnetic storage devices. GENERAL ELECTRIC CO. Ltd. May 28, 1959 [May 28, 1958], No. 17015/58. Class 38 (2). [Also in Groups XIX and XXXIX] In a matrix data store in which thin magnetic films with a thickness in the range of 300 to 3000 Angstrom units are associated with column and row conductors, each film has its preferred axis along which it exhibits uniaxial anisotropy and two alternative remanent magnetization states arranged parallel to the column conductors. As shown in Figs. 1 and 2, magnetic thin films 1 of a nickel-iron alloy which may include molybdenum or copper are deposited in rows and columns on a glass base 2. Printed circuit boards 3, 4, 5, 6, 7, 8 carrying copper electrodes 9a, 9b, 10a, 10b, 11a, 11b are arranged on the two sides of the glass base, pairs of electrodes such as 9a, 9b being joined together at one end to provide single turn read-out, row and column windings 9, 10 and 11, respectively. It is stated that two modes of magnetization state reversal by a magnetic field applied along the preferred axis by current in a row conductor are possible. In one mode a magnetic field of sufficient magnitude switches the remanent state by direct rotation. In the alternative mode a magnetic field of lesser value causes a slow switching by the growth of reverse domains. In this arrangement the row current applied is of such value as to be unable to effect switching in either mode by itself. This current passes through a row winding in one or other direction according to the binary value of a signal applied to an associated input circuit 12. During the period when row current is flowing, a current is applied from a control circuit 15 to a selected column conductor, this current being of a value in excess of 0.6 of the current necessary to saturate a film in a direction perpendicular to its preferred axis. The combined effect of the coincident currents in a row and column is to reverse the remanent state of a film (if its existing remanent state permits) by direct rotation. Examples of current values are: row 100 mA. and column 1A. A read-out pulse is induced in the winding 9 which is detected as to polarity by a circuit 17. Non- destructive read-out may also be effected by using a column current of one-half the previous magnitude. In this case no reversal of remanent state occurs, but a flux change occurs temporarily which induces pulses in conductor 9 corresponding to the leading and trailing edges of current in conductor 11. The remanent state is distinguishable by the relative polarities of these pulses. According to the Provisional Specification, gold electrodes may be used, and the films 1 may be coated with a silicon monoxide or magnesium fluoride layer. Specification 919,021 is referred to.